I understand that they want a person to do it that way but I am asking why -
This is the way DC works. It does not have to make sense and rarely does.
You buy a plan based on where SS thinks you live. You can only have ONE primary residence. If you are a snow bird, pick one place. You can always change it but that does not entitle you to a new Medigap plan.
PDP, yes, but not Medigap.
If you change your residence your existing plan will follow you. If you want to buy a new plan in your new home you can.
As long as you pass underwriting.
Federal (CMS) rules trump everything. States (like MA) can/did petition CMS to offer their own plans vs the 10 standardized ones. States like CA (birthday rule) and MO (anniversary rule) are free to make their own rules as long as they are not more restrictive than CMS rules.
Everything works that way. Not just insurance.
Guaranteed renewable as long as you pay your premium and the carrier does not go belly up . . . which AFAIK has never happened.
CMS sets rules for Medicare qualifying if you are under 65 but there is no federal requirement regarding U65 Medigap.
Some states require carriers to offer U65 Medigap but that didn't work out so well. Almost no one can afford them so most U65 either buy an MA plan or cruise with OM only.
DC required all carriers writing U65 individual major med to issue policies on a guaranteed issue basis. As a result rates are 3x to 4x (or more) higher than pre-2014. Deductibles and OOP are also 2x or more than pre-2017. Most parts of the country have 3 carriers or less vs 20+ prior to 2014. Almost all U65 plans are now HMO. Very difficult to find a PPO.
If you like your doctor . . . .
If you want to see Medicare go the way of Obamacare keep asking for more hope and change.
Bark less. Wag more.